JPH11106422A - Production of polyethylene for blow molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a polyethylene suitable for using in blow molding by using a single catalyst based on chromium. SOLUTION: This invention relates to a method for producing a support-type catalyst based on chromium and suitable for producing a highdensity polyethylene. The catalyst is obtained by (a) preparing an alumina-containing support, (b) generating a catalyst based on chromium by depositing a chromium compound on the support, (c) removing physically adsorbed water by heating the catalyst at least 300 deg.C in a dried inert gas atmosphere, (d) generating a titanated catalyst based on chromium by titanating the catalyst based on chromium at least 300 deg.C in a dried inert gas atmosphere containing a titanium compound expressed by Rn Ti(OR')m and (RO)n Ti(OR')m R and R' are each a 1-12C hydrocarbyl group, (n) is 0-3, (m) is 1-4 and (m+n) is 4} (containing titanium in an amount of 1-5 wt.% based on the weight of the titanated catalyst) and (e) activating the titanated catalyst at 500-900 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for producing a chromium-based catalyst for use in the production of polyethylene suitable for use in blow molding, a method for producing polyethylene using said catalyst, and the use of said catalyst.

[0002] It is well known that polyethylene is used in the manufacture of blow molded articles, such as bottles. Polyethylene resin made for use in the production of blow molded articles must have the following properties: (a) the resin has physical properties such that the resulting blow molded article has the required physical properties; It is known in the art that it is necessary to achieve a balance of resin having processing properties that can be easily processed into blow molded articles. In order to achieve good processability for such polyethylene resins, it is desirable to improve the flow characteristics and shear response of the polyethylene by broadening the molecular weight distribution of the polyethylene. Furthermore, when this solid resin is used in a blow molded bottle, the resin has a high density and a high environmental stress crack resistance.
less cracking resistance)
It is necessary to give it the property of showing (ESCR).

[0003] In general, the higher the density of polyethylene, the higher the degree of stiffness, which is more suitable for producing bottles by blow molding. In known polyethylenes, the higher the stiffness, the higher the strength of the bottle, which allows for the use of thinner wall thicknesses. However, in general, the environmental stress crack resistance exhibited by polyethylene is inversely related to hardness. In other words, the environmental stress crack resistance of polyethylene decreases with increasing hardness, and vice versa. Such an inverse relationship is known in the art as ESCR-stiffness balance. For a given bottle grade of polyethylene, it is necessary to achieve a compromise between the environmental stress crack resistance exhibited by the polyethylene used in blown bottles and the rigidity of the polyethylene. Polyethylene, suitable for use in blow molding
Many different catalyst systems have been disclosed, especially for the production of high density polyethylene (HDPE). It is known in the art that the physical properties, especially the mechanical properties, of a polyethylene product vary depending on what catalyst system is used in the production of the polyethylene. This is due to the fact that the molecular weight distribution of the resulting polyethylene tends to be different when different catalyst systems are used. It is known to use chromium-based catalysts (ie catalysts known in the art as "Phillips catalysts"). The use of such chromium-based catalysts can result in polyethylene exhibiting desirable physical properties and fluidity.

[0004] It is known in the art to use chromium-based catalysts in the polymerization of HDPE, particularly in the production of high density polyethylene which exhibits high environmental stress crack resistance. For example, EP-A-0291824, EP-A-0591968 and U.S. Pat.
No. 310,834 discloses mixed catalyst compositions incorporating a chromium-based catalyst in the polymerization of polyethylene. Each of these conventional proposals has the disadvantage that the complexity of the process and the cost of the process can be increased due to the need for a mixed catalyst.

[0005] The incorporation of titanium in chromium-based catalysts is known in the art. Titanium can be incorporated into the chromium catalyst support or can be incorporated into the catalyst composition attached to the support.

[0006] Cogel and tergel developed by Phillips Petroleum
co-precipitation or tri-precipitation (ter)
Precipitation allows for the incorporation of titanium into the support. Cogel and tergel catalysts are supported on binary and ternary supports, respectively.

Further, for example, US Pat. No. 4,402,86
The support may be impregnated as described in U.S. Pat. No. 4,016,098, or a titanium compound may be chemically absorbed (c) onto the support as described, for example, in U.S. Pat.
It is also possible to incorporate titanium into the support through hemisorption.

[0008] Titanati of the catalyst composition
on) have been disclosed in earlier patent specifications.

US Pat. No. 5,006,506 discloses a titanated catalyst based on silica or chromium supported on a silica / alumina support, in which the catalyst is dried and dried. After that, prior to activation of the catalyst, the dried catalyst is subjected to titanation by treatment with tetraisopropyl titanate.

US Pat. No. 4,718,703 discloses the addition of a titanium compound of the formula Ti (OR) ₄ to a composite liquid suspension containing a carrier material (ie, a support) and chromium trioxide. Discloses that titanium can be incorporated into the catalyst composition.

US Pat. No. 4,224,428 discloses the titanation of a chromium-based catalyst supported on a silica support, wherein the catalyst is converted to a liquid tetrahydrate after a drying step. It has been treated with isopropoxide and then activated.

US Pat. No. 4,184,979 discloses the addition of a titanium compound, such as titanium tetraisopropoxide, at an elevated temperature to a chromium-based catalyst which has been heated in a dry inert gas. It is disclosed that titanium can be incorporated into the catalyst composition. Next, the titanation catalyst is activated at a high temperature.

US Pat. No. 3,798,202 discloses the preparation of a chromium-based titanation catalyst suitable for use in the production of low density polyethylene.

It is an object of the present invention to provide a process for producing polyethylene suitable for use in blow molding using a single chromium-based catalyst.

It is a further object of the present invention to provide such a process which provides a blow molded grade of polyethylene which exhibits a good balance of flow and mechanical properties.

It is a further object of the present invention to provide a method for providing blow molded grade polyethylene which exhibits a good balance of environmental stress crack resistance and stiffness.

Accordingly, the present invention relates to a method for polymerizing ethylene or for mixing ethylene with alpha-alkyl having 3 to 10 carbon atoms.
Provided is a method of preparing a chromium-based supported catalyst suitable for use in high density polyethylene production by copolymerizing an olefin comonomer, the method comprising: a) providing an alumina-containing support;
b) attaching a chromium compound to the support to produce a chromium-based catalyst; c) subjecting the chromium-based catalyst to at least 300 ° C. in a dry inert gas atmosphere.
The physically adsorbed water is removed by heating the catalyst to a temperature of 3 ° C. to d) and d) converting the chromium-based catalyst to R _n Ti (OR ′) _m and (RO) _n Ti (O
R ') _m wherein R and R' are the same or different and are hydrocarbyl groups containing from 1 to 12 carbon atoms, n is from 0 to 3, m is from 1 to 4, and m + n is Titration at a temperature of at least 300 ° C. in a dry inert gas atmosphere containing a titanium compound represented by a general formula selected from the group consisting of a chromium-based titanation catalyst. However, the titanation catalyst is 1 to 5 based on the weight of the titanation catalyst.
Weight percent titanium content, and e) activating the titanation catalyst at a temperature of 500 to 900 ° C.

The present invention also provides a method for producing a high density polyethylene suitable for use in blow molding, wherein the method comprises polymerizing ethylene in the presence of a catalyst formed according to the present invention. 3 to 1 carbon atoms
The above production is carried out by copolymerizing 0 alpha-olefin comonomer.

The present invention also relates to a process for producing high density polyethylene suitable for use in blow molding, which process involves polymerizing ethylene or copolymerizing ethylene with an alpha-olefin comonomer having 3 to 10 carbon atoms. The present invention also provides the use of the catalyst produced according to the present invention in the process of the present invention for the purpose of improving the environmental stress cracking resistance of a polyethylene resin.

The present invention uses a combination of special processing steps to prepare and use a special catalyst system containing a chromium-based catalyst supported on an alumina-containing support and having a titanated surface. It has been surprisingly found by the present inventors that blow-molded grades of polyethylene exhibiting improved mechanical properties, especially improved ESCR-rigidity equilibrium, when compared with other chromium-based catalysts. Based on what you find.

The high-density polyethylene is preferably 1
Shows the Bell ESCR F50 value over 00 hours.

[0022] Such an improvement in processing performance is achieved by using ESCR-
This is the result of enhancing the shear response by broadening the molecular weight distribution while maintaining the stiffness balance equally well.

The preferred chromium-based catalyst includes chromium oxide, which is supported on a silica-alumina support. The support preferably contains 0.75 to 6% by weight of aluminum, more preferably 2 to 4% by weight of aluminum, and most preferably about 2 to 4% by weight of aluminum, based on the weight of the chromium-containing catalyst. % By weight. The catalyst preferably contains at least 0.5% by weight of chromium, more preferably 0.5 to 5% by weight, most preferably about 1% by weight, based on the weight of the chromium-containing catalyst.
The catalyst has 200 to 700 m ² / g, preferably 275
To 500 m ² / g, most preferably about 350 m ² / g, and more than 1 cc / g, preferably about 1.5 to 3 cc / g, most preferably about 2.5 cc / g. To 2.7 cc / g of pore volume. Particularly preferred catalysts have a pore volume of at least ^2.5 cc / g and a specific surface area of at least 275 m ² / g.

A chromium-based catalyst ("catalyst 1") which is particularly suitable for use in the present invention has the following properties:
About 2.1% by weight of Al on a SiO ₂ and Al ₂ O ₃ support
Volume, 2.7 cc / g pore volume and 360 m ² / g specific surface. A suitable alternative for use in the present invention, catalysts based on chromium ( "catalyst 2"), to have the following properties: SiO ₂ and Al ₂ O ₃ about 0.76 wt% to the support of Al ₂ amount, chromium content of about 0.5% by weight, 2.5
It has a pore volume of cc / g and a specific surface of 388 m ² / g.

The chromium-based catalyst is pretreated to drive physically adsorbed water out of the silica-alumina support, ie, the Si-O-framework of the support (no need to be removed). ) Is attached to the hydroxide (-
The dehydration is carried out by driving off the water which is chemically adsorbed in the form of OH) groups. The removal of this physically adsorbed water avoids the formation of TiO ₂ as would occur from the reaction of water with a titanium compound introduced later during the titanation procedure as described below. The dehydration step,
Suitably, the catalyst is carried out by heating the catalyst to a temperature of at least 300 ° C. in a dry inert atmosphere, such as a nitrogen atmosphere, in a fluidized bed. This dehydration step is preferably performed at 0.
Perform for 5 to 2 hours.

The dehydrated catalyst is then subjected to a titanation step, preferably in a fluidized bed and in a high temperature inert atmosphere, to decompose the titanium-containing compound at a high temperature and convert the titanium to the catalyst. To adhere to the surface. This titanium compound has the formula R _n Ti (OR ′) _m or (RO) _n Ti (O
R ') _{m wherein} R and R' are the same or different and may be any hydrocarbyl group containing from 1 to 12 carbon atoms, n is from 0 to 3, and m is from 1 to 4 , And m + n is equal to 4].
The titanium compound is preferably titanium tetraalkoxide Ti (OR ') _{4 where} R' may be an alkyl or cycloalkyl group each having 3 to 5 carbon atoms. . This titanation is carried out by gradually introducing the titanium compound into the dry inert non-oxidizing gas stream described in the dehydration step described hereinabove while maintaining at least 300 ° C. Preferably,
The titanium compound is pumped as a liquid to a reaction zone and vaporized in that zone. The titanium as described above such that the titanium content of the resulting catalyst is suitably 1 to 5% by weight, preferably 2 to 4% by weight, based on the weight of the chromium-based titanated catalyst. Adjust the chemical stage. Calculate the total amount of titanium compound introduced into the gas stream so as to obtain the required titanium content in the resulting catalyst, and progress the titanium progressively so that the titanation reaction period is 0.5 to 1 hour. Adjust the flow rate.

After the completion of the introduction of the titanium compound at the end of the reaction period, the catalyst is washed with a flash (f).
rush) under a stream of gas, typically for 0.75 hours.

The dehydration and titanation steps are performed in the gas phase in a fluidized bed.

While not wishing to limit the scope in theory, it is believed that titanium is chemically bonded to the -Si-O- framework of the support.

The chromium-based catalyst is preferably activated at an elevated temperature, preferably from 500 to 900 ° C, more preferably from 550 to 750 ° C, and most preferably about 650 ° C.

In a preferred method according to the invention, the polymerization or copolymerization step is carried out in the liquid phase in the case of ethylene and the copolymerization with an α-olefin comonomer containing 3 to 10 carbon atoms is carried out. Makes it present in an inert diluent. The comonomer is 1-butene, 1-pentene,
It can be selected from 1-hexene, 4-methyl 1-pentene, 1-heptene and 1-octene. The inert diluent is preferably isobutane. This polymerization or copolymerization process is typically carried out at 85 to 110 ° C, most preferably at 9 ° C.
It is carried out at a temperature of 5 to 105 ° C. The polymerization or copolymerization process is preferably carried out at a pressure of from 20 to 45 bar, most preferably from 40 to 42 bar. The polymerization process typically involves ethylene monomer in an inert diluent for 0.5
To about 8% by weight, typically about 6% by weight of the total weight of ethylene. In the copolymerization process, the ethylene comonomer typically comprises 0.5 to 6% by weight in the inert diluent and the comonomer is 0.5 to 3% by weight, based on the total weight of the ethylene monomer and the comonomer. To be configured.

In the method of the present invention, the above-mentioned chromium-based catalyst which has been activated by titanation is introduced into a polymerization reactor. The alkylene monomer and, where appropriate, the comonomer are charged to the polymerization reactor in an inert diluent, and hydrogen gas is also introduced to the polymerization reactor. The polymerization product, high density polyethylene, is removed from the reactor and the diluent is separated therefrom, which can then be reused.

The polyethylene resin produced according to the method of the present invention has properties which are particularly suitable for use as blow molding grade polyethylene. In the method of the present invention,
In particular, 10 to 60 g / 10 ', preferably 15 to 35
g / 10 'high melt index (HML)
The polyethylene resin can be produced in the form of pellets showing I) and a melt index (MI ₂ ) in the range of 0.02 to 0.5 g / 10 ′. Both the high load melt index HMLI and the melt index MI ₂ were 21.6 each according to the procedure of ASTM D1238.
1 is a melt index measured at a temperature of 190 ° C. using a load of 2.16 kg. Furthermore, the shear response (which is the ratio between HMLI value and MI ₂ values, serve to explain the workability indicated polyethylene resin caused in accordance with the method of the present invention) are diverse ranging from 80 to 200 possible.

The method of the present invention also makes it possible to produce polyethylene resins which exhibit a good compromise between ESCR and rigidity. Bell ESCR (50 ° C 100
% Antarox) to ASTM D
It was measured according to Procedure B of -1693-70.

For the purpose of demonstrating the preferred method of the present invention using a chromium-based catalyst in the polymerization of polyethylene, several experiments were conducted from Example 1 to produce high density polyethylene by homopolymerization and copolymerization of ethylene. 3 was carried out.

[0036]

EXAMPLE 1 In this example, a liquid containing ethylene and 1-hexene, the balance being isobutane as inert diluent, was polymerized at a polymerization temperature of about 102 ° C. under a pressure of about 40 bar. Sent to the zone. Hydrogen was also fed into the polymerization reaction zone. In Example 1, the catalyst system included a chromium-based catalyst ("Catalyst 1") and had been subjected to a pretreatment including dehydration, titanation and activation.

The above dehydration, titanation and activation steps were performed as follows. The chromium-based catalyst was introduced into an activator vessel incorporating a fluidized bed, flushed under nitrogen and then the temperature was raised from room temperature to 300 ° C. Next, a dehydration step was performed at this elevated temperature for 2 hours.
After this dehydration step, titanium tetraisopropoxide (stored under anhydrous nitrogen) was slowly injected into the bottom of the activator vessel incorporating the fluidized bed. Calculate the amount of titanium tetraisopropoxide injected to achieve the required titanium content in the resulting catalyst, and ensure that the desired level of titanation is completed in about 30 minutes as the injection continues. Adjusted its flow rate. After this injection was completed, a flash flush of the catalyst was performed under nitrogen for about 4 hours.
Performed for 5 minutes. Next, the next activation phase 1 was performed by gradually switching the nitrogen to air and raising the temperature to the activation temperature of about 650 ° C. In this activation stage, the chromium-based titanated catalyst was held at the activation temperature for 6 hours. At the end of this activation phase, the temperature was gradually reduced to 350.degree. The catalyst was flushed under nitrogen while continuing to cool from 350 ° C. to room temperature.

The polymerization conditions and the properties of the resulting polyethylene product are summarized in Table 1.

Comparative Example 1 Comparative Example 1 was carried out using the same catalyst "catalyst 1" except that the catalyst was not subjected to any dehydration or subsequent titanation. Instead, alkylboron, especially triethylboron (TEB), was added to the above catalyst. This TEB was placed in an inert diluent and introduced into the polymerization reactor so that it comprised 0.6 ppm based on the weight of the inert diluent. TEB was used for the purpose of increasing the activity of the catalyst so as to increase the processing yield. The HMLI and density of the polyethylene pellets obtained in Comparative Example 1 are the same as those of Example 1, but the Bell ESCR (50 °
100% Antalox) will be found to be 78 hours.

The comparison between the Bell ESCR value of Example 1 and the Bell ESCR value of Comparative Example 1 shows that the use of an alumina-containing support in combination with a titanated surface without using an organic boron compound and the polyethylene resin It clearly demonstrates that environmental stress crack resistance can be better.

While not wishing to limit the scope in theory, it is believed that when alumina is applied to the support when the chromium-based catalyst is supported on a silica-containing support, a high molecular weight fraction is generated in the polyethylene resin. . If this catalyst is subjected to dehydration and titanation to give it a titanized surface, then a good low molecular weight fraction is generated in the polyethylene resin, which broadens the overall molecular weight distribution.
In this way, a polyethylene resin exhibiting good environmental stress crack resistance characteristics is obtained. Although the HLMI and density of the polyethylene resins obtained in Comparative Example 1 and Example 1 were substantially the same, when the titanation was used in the catalyst of the present invention, T
In contrast to Comparative Example 1 with EB, instead of undergoing a pretreatment with dehydration and titanation according to the invention, TE
It can be seen that unexpectedly improved environmental stress cracking resistance is obtained compared to using substantially the same catalyst except for the addition of B.

Example 2 In this example, the product of the reaction of chromium (III) acetylacetone and triisobutylaluminum (TIBAL) in hexane is commercially available from Grace GmbH (Worms, Germany). Trademark G
The preparation of the Cr / SiAl-oxide catalyst was carried out after treating the silica support sold under race G5H, drying and stabilizing with low-temperature air. The final catalyst composition contains 1% by weight of Cr and 2% by weight of Al, both of which are weight percentages based on the weight of the catalyst. Next, the catalyst was activated and titanated in the following procedure.
The catalyst was heated from room temperature to 300 ° C. under nitrogen while the catalyst dried. While maintaining the catalyst at 300 ° C., a gaseous mixture of nitrogen and titanium triisopropoxide was injected. Next, the catalyst was placed in air at 300 to 6
Heat to 50 ° C. and hold at 650 ° C. for 6 hours. afterwards,
The catalyst was cooled first under air and then under nitrogen. The final titanium content was 4% by weight of Ti, based on the weight of the catalyst.

The activated catalyst was then tested by ethylene polymerization using a 4 liter autoclave reactor. The polymerization took place in a diluent consisting of 2 liters of isobutane. The total pressure in the autoclave reactor was established so that ethylene dissolved in 6% by weight of this isobutane. In all of the multiple experiments, the polymerization temperature was 9
In the range of 8 to 106 ° C., and also in some experiments homopolymerization to produce polyethylene, and in other experiments, polyethylene was introduced by copolymerization by introducing 0.5% by weight of 1-hexene in isobutane to an autoclave reactor. Manufactured. Catalytic activity was established such that about 1000 g of PE was produced per gram of catalyst. By adjusting the polymerization temperature to about 0.1.
It was possible to obtain a final melt index MI ₂ the range of 15 to about 0.25 g / 10 min. Table 2 shows the properties of the polymers produced according to this example. Example 1
As in the case of the above, the ESCR of one of the homopolymers
And measuring the ESCR of one of the copolymers,
Table 2 shows the results.

Comparative Example 2 In this comparative example, Example 2 was essentially repeated except that no titanation step was included during catalyst activation. In other words, the catalyst is activated in a nitrogen atmosphere at room temperature for 3 hours.
Heat to 00 ° C and then heat the catalyst in air at 300-650 ° C
And then holding the catalyst at 650 ° C. for 6 hours. Next, the catalyst was cooled first under air and then under nitrogen. This catalyst was used in the manner described hereinabove with reference to Example 2 to produce homopolymers and copolymers of polyethylene. Table 2 also shows the properties of the obtained polymer.

The use of titanation of the catalyst in Example 2 resulted in the melt index potential (mel) of the catalyst.
It can be seen from Table 2 that the t index potential is improved. At a given polymerization temperature, both the homopolymers and the copolymers can obtain the MI ₂ value obtained when the titanation catalyst of Example 2 is used when the untitanized catalyst is used. It can be seen that there is a tendency to be higher than the MI ₂ value. The shear response (SR ₂ ) of the resin obtained when using the titanated catalyst according to Example 2 was high despite the higher melt index obtained. From this, as a result, the processability of the polyethylene resin will be better. FIG. 1 shows the relationship between the shear response SR ₂ and the melt index MI ₂ obtained in various experiments of Example 2 and Comparative Example 2. It will be seen that with a titanated catalyst according to the present invention, not only can a higher melt index be achieved, but also for a given melt index, the shear response tends to be higher.

In addition, the use of the titanated catalyst of Example 2 leads to a decrease in ESCR / density as compared to the case of using the catalyst of Comparative Example 2 not subjected to titanation. improves. Such an improvement is due to the density and E of the catalyst of Example 2 and the catalyst of Comparative Example 2 used.
FIG. 2 shows the relationship between the SCR values.

Example 3 In this example, a different catalyst synthesis route was used to
An R / SiAl-oxide catalyst was prepared. In this example, the dry silica carrier Gra
ce G5H was reacted with TIBAL in hexane solution, dried and stabilized by air. Next, acetylacetone chromium (III) [C
r (acac) ₃ ] and rotavapor (rot
After drying on an avapour, it was finally dried in an oven at 80 ° C. The final catalyst composition was similar to that of Example 2 except that the color of the catalyst was blue instead of green. The catalyst was activated using a titanation treatment in the same manner as described hereinabove with reference to Example 2. The target titanium content is 4 based on the weight of the catalyst.
It was titanium by weight.

Using the same polymerization conditions specified in Example 2, the titanated and activated catalyst was tested for homopolymerization of ethylene. Table 3 shows the results.

Comparative Example 3 In Comparative Example 3, a catalyst was prepared in a manner similar to that of Example 3, except that the titanation step was omitted in the activation treatment. Again, using the same conditions as in Example 3, the activated catalyst was tested for ethylene homopolymerization. Table 3 shows the results.

It can be seen from Table 3 that the use of the titanated catalyst according to the present invention not only significantly improves the melt index of the polyethylene homopolymer, but also improves the shear response of the resin.

[0051]

[Table 1]

[0052]

[Table 2]

[0053]

[Table 3]

The features and aspects of the present invention are as follows.

1. A process for producing a chromium-based supported catalyst suitable for use in the production of high density polyethylene by polymerizing ethylene or copolymerizing ethylene with an alpha-olefin comonomer having 3 to 10 carbon atoms. A) providing an alumina-containing support; b) adhering a chromium compound to the support to produce a chromium-based catalyst; c) subjecting the chromium-based catalyst to a dry inert gas atmosphere. Dewatering the catalyst by heating to a temperature of at least 300 ° C. in water to remove physically adsorbed water; d) converting the chromium-based catalyst to R _n Ti (OR ′) _m And (RO) _n Ti (OR ') _m [where R and R'
Are the same or different and are hydrocarbyl groups containing from 1 to 12 carbon atoms, n is from 0 to 3, and m is 1
To 4 and m + n is equal to 4] by titanating at a temperature of at least 300 ° C. in a dry inert gas atmosphere containing a titanium compound represented by the general formula selected from Wherein the titanation catalyst has a titanium content of 1 to 5% by weight, based on the weight of the titanation catalyst, and e) converts the titanation catalyst to 500 to 900 Activating at a temperature of 0 ° C.

2. At least 275 m ² /
2. The method according to claim 1, which has a specific surface area of g.

3. The titanium compound has the general formula Ti (O
R ') _{4 wherein} R' is selected from alkyl and cycloalkyl each having 3 to 5 carbon atoms.
3. The method according to item 1 or 2, which is a titanium tetraalkoxide represented by the formula:

4. 4. The method according to any one of claims 1 to 3, wherein the titanation catalyst has a titanium content of 2 to 4% by weight based on the weight of the titanation catalyst.

5. Items 1 to 4 wherein the chromium compound is chromium oxide and the chromium content ranges from 0.5 to 1.5% by weight, based on the weight of the chromium-based catalyst before titanation. A method according to any one of the preceding claims.

6. A process according to any one of the preceding claims wherein the catalyst comprises from 0.75 to 6% by weight of aluminum in the alumina-containing support, based on the weight of the catalyst.

7. A process according to any of claims 1 to 6, wherein the catalyst comprises 2 to 4% by weight of the aluminum in the alumina-containing support, based on the weight of the catalyst.

8. A process for producing high density polyethylene suitable for use in blow molding, comprising polymerizing ethylene in the presence of a chromium-based catalyst produced according to any one of paragraphs 1 to 7, or A method comprising copolymerizing ethylene and an alpha-olefin comonomer having 3 to 10 carbon atoms.

9. A method for producing a high density polyethylene suitable for use in blow molding, comprising polymerizing ethylene or copolymerizing ethylene with an alpha-olefin comonomer having 3 to 10 carbon atoms. Use of a catalyst system produced according to any one of the preceding clauses for the purpose of improving the environmental stress cracking resistance of polyethylene resins.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the shear response and the melt index of a polyethylene resin produced according to Example 2 and Comparative Example 2.

FIG. 2 is a graph showing the relationship between density and ESCR of polyethylene resins produced according to Example 2 and Comparative Example 2.

Claims (3)

[Claims] 1. A supported chromium-based catalyst suitable for use in the production of high density polyethylene by polymerizing ethylene or copolymerizing ethylene with an alpha-olefin comonomer having 3 to 10 carbon atoms. A method of manufacturing comprising: a) providing an alumina-containing support; b) attaching a chromium compound to the support to produce a chromium-based catalyst; c) providing the chromium-based catalyst. The catalyst is dehydrated by heating to a temperature of at least 300 ° C. in a dry inert gas atmosphere to remove physically adsorbed water. D) This chromium-based catalyst is converted to R _n Ti (OR ') _m and (RO) _n Ti (OR') _m [where R and R '
Are the same or different and are hydrocarbyl groups containing from 1 to 12 carbon atoms, n is from 0 to 3, and m is 1
To 4 and m + n is equal to 4] by titanating at a temperature of at least 300 ° C. in a dry inert gas atmosphere containing a titanium compound represented by the general formula selected from Wherein the titanation catalyst has a titanium content of 1 to 5% by weight, based on the weight of the titanation catalyst, and e) converts the titanation catalyst to 500 to 900 Activating at a temperature of 0 ° C. 2. A process for producing a high density polyethylene suitable for use in blow molding, comprising polymerizing ethylene in the presence of a chromium-based catalyst formed according to claim 1 or comprising ethylene and carbon. A method comprising copolymerizing an alpha-olefin comonomer having 3 to 10 atoms. 3. A process for producing high density polyethylene suitable for use in blow molding, comprising polymerizing ethylene or copolymerizing ethylene with an alpha-olefin comonomer having 3 to 10 carbon atoms. Use of the catalyst system produced according to claim 1 for the purpose of improving the environmental stress crack resistance of polyethylene resins.